The present invention generally relates to an electromagnetic wave absorbing technique and also an electronic appliance with employment of this electromagnetic wave absorbing technique. More specifically, the present invention is directed to such a technique capable of lowering, or reducing emission noise, e.g., EMI (electromagnetic interference).
While various sorts electronic appliances are widely marketed which are typically known as, for instance, desk-top type personal computers, portable type personal computers, and furthermore, mobile communication terminals, e.g., portable telephones, various types of electromagnetic noise waves so-called as xe2x80x9cEMIxe2x80x9d are emitted,or radiated from these various electronic appliances. As a result, since these unwanted electromagnetic noise waves may cause environmental pollution, this fact may cause a serious problem. To avoid such environmental pollution, voluntary controls, e.g., the FCC VCCI rules are established by electronic appliance industries.
The conventional techniques capable of reducing EMI noise emitted from electronic appliances are known as follows. For instance, as described in JP-A-7-22244, the emission noise is absorbed by the resonant circuit having the resonant frequency defined by the inductance xe2x80x9cLxe2x80x9d and the capacitance xe2x80x9cCxe2x80x9d.
Also, JP-A-7-240595 discloses the following EMI reducing technique. That is, on the printed board, the signal line and the power supply line, the ground layer, and furthermore, the frame-shaped frame ground pattern are sandwiched along the upper/lower directions by employing both the frame ground solid pattern made of the conductor and the ground plane made of the conductor in order that the electromagnetic waves emitted from the signal line, the power supply line, and the ground layer are shielded.
However, the first-mentioned conventional EMI reducing technique owns the below-mentioned technical problem. That is, while electronic circuits are operable under high speeds and are manufactured in high integration (with employment of very fine techniques), it is practically impossible to set such a resonant circuit in the vicinity of emission noise producing sources because of physical limitations.
The last-mentioned conventional EMI reducing technique has the following technical problem. Although this conventional electromagnetic wave shielding technique may have the advantageous effect with respect to the EMI noise produced within the printed circuit board, this shielding technique cannot have particular advantages as to the EMI noise produced from the IC and the LSI mounted on this printed circuit board, and furthermore, the EMI noise emitted from such an electronic appliance equipped with this printed circuit board.
The present invention has been made to solve these conventional problems, and therefore, has an object to provide a technique capable of firmly suppressing noise emitted from an electric/electronic appliance in a simple manner.
Another object of the present invention is to provide a technique capable of firmly suppressing noise emitted from an electric/electronic appliance in low cost.
A further object of the present invention is to provide a technique capable of suppressing noise emitted from various appliances having various shapes/dimensions and operable under various use environment.
In accordance with the present invention, it is provided such electromagnetic wave absorbing device comprising:
a first member having a resistor having a resistance value smaller than, or equal to several ohms; and
a second member having a resistor having a resistance value larger than, or equal to several ohms, and connected so as to form an electric loop in combination with the first member.
Also, in accordance with the present invention, there are provided both an electronic apparatus manufacturing method and an electronic apparatus comprising:
a circuit apparatus; and
an electromagnetic wave absorbing device arranged in the vicinity of the circuit apparatus in an insulating manner with respect to a circuit of the circuit apparatus, and having a metal loop, a portion of which is made of a high resistor.
Furthermore, it is preferable such that a portion of the high resistor has a resistance value higher than, or equal to 20 ohms and lower than, or equal to 200 ohms, whereas the remaining portion of the metal loop has a resistance value lower than, or equal to 1 ohm.
Also, in accordance with the present invention, it is possible to provide such an electromagnetic wave absorbing method wherein:
electric energy induced in an antenna portion by an electromagnetic wave is converted into thermal energy by a resistor portion connected to the antenna portion, whereby the electromagnetic wave is attenuated.
Also, according to the present invention, it is provided such an electromagnetic wave absorbing device comprising: an electromagnetic wave absorbing structure containing an antenna portion resonated with an electromagnetic wave; and a resistor portion series-connected to the antenna portion.
Further, according to the present invention, it is provided such an electronic component comprising: an electromagnetic wave absorbing structures containing an antenna portion resonated to an electromagnetic wave; and a resistor portion series-connected to the antenna portion.
In this electromagnetic wave absorbing device, the antenna portions of the electromagnetic wave absorbing structures are connected to both ends of the resistor portion; and each of these antenna portion is constituted by one pair of dipole antennas. The dipole antenna has a length substantially equal to a xc2xc wavelength of the electromagnetic wave.
Also, according to the present invention, the antenna portion of the electromagnetic wave absorbing structure is constituted by a loop antenna connected to both ends of the resistor portion; and the loop antenna has a length which is resonated with the electromagnetic wave.
Preferably, such an electromagnetic wave absorbing device is mounted on a flexible insulating film member having an adhesive surface. Then, this electromagnetic wave absorbing device may be mounted via this adhesive surface on a desirable electronic appliance, and may be therefore mounted on an arbitrary position. Also, in such a case that the electromagnetic wave absorbing device is mounted on the insulating film member, the antenna portions of the electromagnetic wave absorbing structures may be cut at any lengths thereof together with this insulating film member. The antenna portion may be set to such an arbitrary length defined by considering the wavelength of the electromagnetic wave to be absorbed. Also, a plurality of electromagnetic wave absorbing structures equipped with antenna portions having different lengths from each other are mounted in one group. As a result, these electromagnetic wave absorbing devices may absorb the electromagnetic waves located within an arbitrary wavelength range.